If you want to use the Advanced Search page specifically, you must use a browser and request the desktop site version of the page. But it is often not necessary to use the Advanced Search page to get some of the same search features if you use the right search syntax.
The eBay app will allow you to do most of the same searches you can with a browser, but you may need to do things a little differently. You can still exclude a keyword by putting a minus sign in front of the word, just as you can on the web site.
If you describe what sort of search you are trying to do, someone may be able to offer some practical suggestions.
If you can set up a search using a desktop browser, you can save the search and in most cases you should be able to use the saved search in the app and get the same results.
Some info about search syntax that works with both browser and app can be found on this old page on eBay Ireland:
https://www.ebay.ie/pages/help/search/search-commands.html
